1. Field of the Invention
The present invention relates to an optical device wafer dividing method for dividing an optical device wafer into individual optical devices along streets formed in a latticelike pattern on the front surface of a substrate such as a sapphire substrate or the like, the optical device wafer being such that the optical devices such as gallium nitride-based compound semiconductors or the like are laminated on a plurality of areas meansed along the streets.
2. Description of the Related Art
An optical device wafer may be meansed into a plurality of areas along predetermined dividing lines called streets formed in a latticelike pattern on the front surface of a sapphire substrate, optical devices such as gallium nitride-based compound semiconductors or the like being laminated on the areas thus meansed. This optical device wafer is divided along the streets into individual optical devices such as light-emitting diodes, which are widely used in electric devices. Before divided along the streets, the optical device wafer mentioned above is ground from its rear face by a grinding device and machined into a given thickness. To achieve the weight reduction and downsizing of electric devices, optical devices have recently been required to have a thickness of 50 μm or less. However, if the optical device wafer is ground to have a thickness of as thin as 50 μm or less, there occurs a problem of cracking.
On the other hand, cutting the optical device wafer along the streets is usually carried out by a cutter rotating a cutting blade at high-speeds. However, since the sapphire substrate is a hard-ground material having high-Mohs hardness, it is necessary to slow down machining speed, which poses a problem of poor productivity. The following method has recently been proposed as a method of dividing a wafer such as an optical device wafer or the like. That is to say, a pulse laser beam having a wavelength capable of being absorbed by the wafer is directed along streets to form laser processing grooves. An external force is applied to the wafer along the laser processing grooves to fracture the wafer along the streets. (See e.g. Japanese Patent Laid-Open No. Hei 10-305420.)
Also the following method is proposed as the method of dividing a wafer such as an optical device wafer along streets. That is to say, a pulse laser beam having a wavelength capable of passing through the wafer is emitted along the street while being focused on the inside of the wafer. This continuously forms an altered layer inside the wafer along the street to lower the strength of the street. An external force is applied to the wafer along the street for fracture. (See e.g. Japanese Patent Laid-Open No. 2008-6492.)
In this way, the optical device wafer is irradiated with a laser beam along the streets of the optical device wafer to form the laser beam processing grooves or altered grooves, and is divided into individual optical devices along the streets formed with the laser processing grooves or altered grooves. In this case, altered materials produced by the laser processing are left on the lateral surfaces (the fracture surfaces) of the individually divided optical devices. This poses a problem of lowering the luminance of the optical device and of reducing die or bending strength.